Process and apparatus for antiskid control mechanism

ABSTRACT

This invention presents an improved method and apparatus for an antiskid brake control which provides the shortest possible brake application period and maximum adhesive force between the vehicle tires and the road surface under all conditions by utilizing an electronic circuit into which input signals representing vehicle speed, wheel speed and hydraulic brake apply pressure are fed. The electronics control circuit computes the rate of vehicle deceleration and the ratio of the wheel speed to the vehicle speed and compares this ratio with a constant value. An output signal from the electronic circuit is used to control an electric solenoid valve in the hydraulic brake circuit to modulate the hydraulic pressure and obtain an optimum vehicle braking effort under all conditions and prevent a vehicle skid condition from arising.

United States Patent 11 1 Kuwana et a1.

[ PROCESS AND APPARATUS FOR ANTISKID CONTROL MECHANISM [75] Inventors: Kazutaka Kuwana, Kariya; Hayao Yamazaki; Takefuini Sato, both of Osaka, all of Japan 211 App]. No.: 82,040

[52] US. Cl. 303/21 P, 303/20, 303/21 BE I [51 16:. c1. B60t 8/10 [58] Field of Search 188/181; 303/20, 303/21; 317/5; 318/52; 324/160-162; 340/262-263 [56] 3 References Cited UNITED STATES PATENTS 3,609,313 9 1971 Lucien 303/21 BE x 3,671,083 6/1972 Matsumura 303/2'1 BE 3,672,730 6 1972 Burckhardt et al 303/21 BE 3,275,384 9 1966 Hirzel 303 21 EB 3,394,967 7/1968 Lucien; ,5. 303 21 BE 3,467,443 9/1968 Okamoto et 8.1.. 303 21 BE 3,498,682" 3/1970 Mueller et al. 303 21 BE 3,583,773

6/1971 Steinbrenner et a1. 303/21 EB Sept. 11, 1973 3,586,386 6/1971 Riordan et a]. 303/21 BE UX FOREIGN PATENTS OR APPLICATIONS 1,810,163 7/1970 Germany 303/21 BE 1,953,253 6/1970 Germany 303/21 P Primary Examiner-Milton Buchler Assistant ExaminerStephen G. Kunin I Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT,

This invention presents an improved method and apparatus for an antiskid brake control which provides the shortest possible brake application period and maximum adhesive'force between the vehicle tires and the road surface under all conditions by utilizing an electronic circuit into which input signals representing vehicle speed, wheel speed and hydraulic brake apply pressure are fed. The electronics control circuit computes the rate of vehicle deceleration'and the ratio of the wheel speed to the vehicle speed and compares this ratio with a constant value. An output signal from the electronic circuit is used to control an electric solenoid valve in the hydraulic brake circuit to modulate'the hydraulic pressure and obtain an optimum vehicle braking effort under all conditions and prevent a vehicle skid condition from arising.

25 Claims, 41 Drawing Figures p -1 WHEEL wHEEL CYLINDER YPRIES CYLINDER SURE REGULATOR'fG PRESSURE-5 J COMPARATOR v wHEEL vEHlcLE' I -J 6 SPEED 6 1 6 WHEEL COMPAFAZOR DECELER- 0.6x VEHICLE'SPEED n .ATION- 6, 5

1 I '-1 1- 1 I v VEHICLE SPEED E VALUE y, WHEEL DECELERATION+ AT MAXIMUM 5 I 0.8x VEHICLE SPEED -5 ADHESIVE COEFFICIENT PRESSURE, P

V PA(LAG o PRiSSURE RESTORATION) PATENTEDSEH nan 3.758.166

sum In or 13 FIG. 3A 26 EH5 WG-| LIJ A 82% V TlME,T- LIJZ 3 0 a; FIG. 38

l LIJ I l I TIME T- M L I PA-| (LAG OF PRESSURE H9 30 g *I I I REDUCTION) m I VA 55 A-l E LLI IF PA-l(LAG 0F PRESSURE n: RESTORATION) 3 c0 91 TIME, T-- LU PA P AIL/AG OF PRESSURE I" INVENTORS KAZUTAKA Kan/ANA TA/(EFl/MI SATO YAMAZ/IK/ ATTORNEYS PATENIEusm 1 m SHEU 02 of FIG. 2

Pmnmwn l 3.758.166

saw on HF 13 wITH SOLENOID S -s TURNED OFF z (RESULTING IN SMALLER PRESSURE REDUCING 9 II AND PRESSURE RECOVERY SPEED FOR wHEEL CYLINDER z PRESSURE) E5 1 6 I! g Z Z 2 WITH SoLENoID s -s g TURNED ON (RESULTING 5 IN LARGE AND RECOVERY SPEED FOR WHEEL g CYLINDER PRESSURE) 4 O .20 4O 6O 80 I00 SLIP RATIO I WHEEL SPEED AT MAX.-

, ADHESIVE COEFFICIENT E VEHICLE VELOCITY U WHEEL VELOCITY T l M E WHEEL SPEED AT MAX. ADHESIVE COEFFICIENT 8B 5 VEHICLE VELOCITY O Q wHEEL VELOCITY TlME- PAIENTED 3.758.166

SHEET '05 0F 13 FIG. 9

g" 2-4 L; 3-4 F 54 r v l l A ll F5 '2 ga RATIO OF WHEEL SPEED WHEEL WHEEL WHEEL TO VEHICLE SPEED AT DECELER 4 CYLINDER MAXIMUM ADHESIVE ATI0N- 4 SPEED PRESSURE-4 COEFFlClENT(ABOUTO.8)-4 to n RATIO OF WHEEL O8+WHEEL DECELERATlON-4 SPEED To VEH'CLE SPEED- 4 SPEED 4 "g" l ,i

- COMPARATOR COMPARATOR 7 SET VALUE-4 REGULATOR 4 |WHEEL (:YLTMBER 5215 55155 1 P" PAIENTEIIWIIWI- I 3.758.166

- VACU SIIIEEI 07 0F I3 ,F l. G. TO WHEEL CYLINDER I I TO ENGINE INTAKE H MANIFOLD As I FROM HYDRAULIC SOLENOID s I I BRAKE PRESSURE ATMOSPHERIC AIR 8 PRESSURE SOLENOID s s4-5(DN) 84 5'5 (OFF) A PREDETERMINED VALUE-'5 WHEEL DECELERATION- PATENIEH 3.758.166

SHEET 08 0F 13 RATIO OF wHEEL SPEED wHEEL WHEEL WHEEL TO, VEHICLE sPEED AT DECELER- SPEED CYLINDER MAXIMUM ADHESIVE ATION 5 5 PRESSURE-5 COEFFICIENT(ABOUT O.8)5 l I F I I I RATIO OF WHEEL 08+ WHEEL SPEED TO VEHICLE VEH'CLE DECELERATION 5 SPEED 5 Y) SPEED-5 n I X SET vALuE COMPARATOR L COMPARATOR 5 11 5 I 5 l r I I {WHEEL CYLINDER PRESSURE L REGULATOR 5 l wHEEL CYLINDER PRES-1. WHEEL suRE REGULATOR- 5 l gggggfig COMPARATOR S WHEEL vEI-IICLE I 6 sPEED s SPEED- s WHEEL Q F Z DECELER- 0.8 VEHICLE SPEED ATION 6, 6

u VEHICLE SPEED sET vALuE WHEEL DECELERATION+ AT MAXIMUM 6 0.8x VEHICLE SPEED 5 ADHESIVE COEFFICIENT PAIENIEn W8 SHEET 10 (IF 13 i 2; T m mlfi E E M (Iv/x II I K V- VI 12 7;

WHEEL DECELERATION-T WHEEL ACCELERATION 7 BASE POTENTIAL AT TRANSISTOR IC-7 BASE POTENTIAL AT TRANSISTOR Til-7 TIME, T

WITH SOLENOID 82-7 TURNED ON WITH SOLENOID NI! Tv 2 Z w E El. F

32-7 TURNED OFF Pmmznwnma -3 .758.l66

SHEEI 11 0F 13 E m-8 Ev-a am-a PI 6 ,lzzzz-a [III-8 8 l w fl q "I WHEEL CYLINDER PRESSUREI $55 l REGULATOR 7 I PRESSURE? L. l

. COMPARATOR 4 WHEEL VEHICLE I 7 SPEED 7 SPEED 7 WHEEL ABSULUTE VALUE OF WHEEL DECELERAT/DN g figggggg 'i VEHICLE SPEED w 0R ACCELERATION -7 ATION 7 7 V v i COMPARATOR TRIANGULAR WHEEL DECELERA T/ON 0R 0 ER 0 1' V5 8 Pmmmm 'm:

saw 12 or FIG. 25

FIG. 23A

VOLTAGE' FIG. 23B

VOIJ'AGE- VOLTAGE--- WHEEL SPEIED AT MAX.

VELOClTY-8 ADHESIVE COEFFICIENT-8 {COLLECTOR POTENTIAL AT TRANSISTOR T -8 @SE POTENTIAL AT TRANSISTOR T T -'-8 BASE POTENTIAL AT TRANSISTOR s, 'h a ""8 g-vT| rH SOLENOID sl-e TURNED ON WITH SOLENOID SI "'8 TURNED OFF u sms POTENTIAL TURNED ON WITH SOLENOID s2 --8 TURNED OFF -WITI'I SOLENOID 82""8 PATENTED E 3.758.166

saw 13 or 13 FIG. 24

. MAX. ADHESIVE ATION -a WHEEL RATIO OF WHEEL SPEED DECELERAT'ONL WHEEL WHEEL TO VEHICLE SPEED AT OR ACCELR- SPEED g S COEFFICIENT 0C 8 I RATIO OF wHEEL oC+WHEEL DECELERATION SPEED To VEHICLE VEHICLE OR ACCELERATION 8 SPEED -8 SPEED "8 I I 'I TRIANGULAR COMPARATOR COMPARATOR WAVES e I[ -a 1 -a WHEEL CYLINDER PRESSURE REGULATOR I"""'"-'---- PROCESS AND APPARATUS FOR ANTISKID CONTROL MECHANISM This invention relates to improvements in and relating to antiskid brake control method for use with powered and wheeled vehicles, especially automotive vehicles, and an apparatus for realization of the same.

The main purpose of the invention is to provide a substantially improved process and apparatus, capable of providing a shortest possible brake application period for the realization of a certain desired degree of vehicle braking effect such as stoppage of a running vehicle, under utilization, as far as possible, of the maximum adhesive force acting between the wheel tire and the traffic surface on which the vehicle is travelling.

A further object is to provide a method and apparatus of the kind above referred to, capable of maintaining the inevitable fluctuation of the vehicle deceleration rate during a brake application period.

These and further objects, features and advantages of the invention will become more apparent when reading the following detailed description of the invention in comparison with the comparative prior art.

In the drawings:

FIGS. lA-lB are a combined chart showing a V-T diagram illustrative of the mutual relationship among the wheel speed VA, wheel peripheral speed VB and 70 percent-pseudo vehicle speed VC, and a corresponding P-T diagram showing the brake pressure PA plotted against time, the both being as conventionally and frequently met with use of a conventional antiskid brake pressure control unit.

FIG. 2 is a wiring diagram of a first embodiment of the pressure control circuit arrangement constituting the main constituent of the brake pressure control unit adapted for carrying out the process according to this invention.

FIGS. 3A-3C are a combined and illustrative chart for clarifying the operation of the pressure control circuit arrangement shown in FIG. 2.

FIG. 4 is a similar view to FIG. 2,-illustrating, however, a second embodiment of the brake pressure control circuit arrangement.

FIGS. 5A-5D are a combined and illustrative chart for clarifying the operation of the said second embodiment.

FIGS. 6A-6B are a combined illustration of a side view of an automotive car which is provided with a fifth wheel for sensing occasional wheel speed, as a third embodiment of the invention, and a simplified circuit adapted for the above purpose.

FIG. 7 is a chart which the general tendency of the adhesive coefficient mu acting between the traffic surface on which an automotive vehicle is running and the wheel, tyre thereof, said coefficient being plotted against the slip ratio S.

FIGS. 8A-8B are a combined and comparative chart illustrative of the performance curves for the conven tional and the inventive brake pressure controller, respectively.

FIG. 9 is a similar view to FIG. 2, illustrative, however, of a fourth embodiment of the invention.

FIGS. 10 and 11 are similar views to FIG. 2, illustrative, however, of fifth and sixth embodiments of the invention, respectively.

FIG. 12 is a schematic sectional view of several working components constituting a brake pressure controller arranged between the conventional master cylinder and the wheel cylinder and adapted for cooperation with the pressure control circuit embodied in any one of theembodiments set forth throughout the specification.

FIG. 13 is a chart showing a representative performance curve of a block shown at VII-5 in FIG. 10 illustrative of the fifth embodiment of the inventive pressure control circuit arrangement.

FIG. 14 is a block diagram showing in its basic form of the fourth embodiment of the pressure control circuit arrangement shown in FIG. 9.

FIG. 15 is a similar view to FIG. 14, illustrative of the fifth embodiment shown in FIG. 10.

FIG. 16 is a chart showing the performance of the comparator II-5 employed in the fifth embodiment shown in FIG. 10.

FIG. 17 is a similar view to FIG. 2, illustrative, however, of a sixth embodiment of the circuit arrangement.

FIG. 18 is a chart illustrative of the performance curve of the comparator lI-6 employed in the sixth embodiment of the circuit arrangement shown in FIG. 1 1.

FIGS. 19 and 20 are similar views to that shown in FIG. 2, illustrative, however, of a seventh and an eighth embodiments of the circuit arrangement, respectively.

FIGS. 21A-21B are a combined chart illustrative of the working mode of the seventh embodiment shown in FIG. 19.

FIG. 22 is a block diagram showing the seventh embodiment in a highly simplified way.

FIGS. 23A-23C are a combined chart for the illustration of the operating performance of the eighth embodiment shown in FIG. 20.

FIG. 24 is a block diagram of the eighth embodiment in a highly simplified manner.

FIG. 25 is a connection diagram of a modified arrangement of blocks VII-7 and VIII-7 in the foregoing seventh embodiment or of blocks VIII-8 and IX-8 in the foregoing eighth embodiment.

FIGS. 26A-26E are illustrative of I several voltage curves appearing in the foregoing nineth embodiment shown in FIG. 25.-

Before entering into the detailed description of several preferred embodiments of the invention, a brief description of the working principles of the conventional comparative process will be given.v

All numerical data such as percent-psuedo vehicle speed, percent (page 12), slip ratio 20 percent, as used throughout the specification are only representative values and thus may be subject to an allowance of plus or minus several percent in each case.

In FIG. 1A, VC-curve represents a 70 percent pseudo-vehicle speed which has been artificially produced from the vehicle deceleration, the brake pressure PA or the like known parameter. When the wheel speed should drop beyond this 70 percent-pseudo-vehicle speed, the brake pressure is subjected to a reduction intentionally. On the contrary, when the wheel speed should exceed above said pseudo-vehicle speed, the brake pressure is intentionally increased. When the wheel, speed drops again beyond the pseudo-vehicle speed by virtue of the said intentional increase of the brake pressure, the brake pressure will be again reduced intentionally, and so on. By this repeated brake pressure increasing and decreasing steps, the brake application is performed, so to speak, in a wavy manner.

For carrying out the antiskid braking system, a wavy brake pressure application performance curve is realized which will fluctuate as at VB in'FIG. 1 at (A) along the 70 percent-pseudo-vehicle speed curve VC. The wheel speed is naturally subjected to an overall reduction in its value during the whole progress of the brake application, until finally the vehicle is brought into its dead stop condition.

According to this control method belonging to the prior art, the reduction of the brake pressure is intended to initiate when the wheel speed drops beyond the said 70 percent-pseudo-vehicle speed.

In this case, however, the practical initiation of the brake pressure reduction is performed practically upon lapse of a time lag normally amounting to 0.02 second.

In order to re-increase the once reduced wheel speed, the brake pressure must be reduced to a certain degree and such a phenomenon will generally observed that even upon reduction of wheel speed beyond the 70 percent-pseudo vehicle speed, the wheel speed will continue to decelerate. As an example, the braked wheel speed may frequently drop beyond the said pseudo-value by a substantial value such as, for instance, -30 km/hr.

On the contrary, a brake pressure re-increase is intended to initiate only upon realization of a higher wheel speed over said 70 percent-pseudo-vehicle speed. In this case, also, a similar kind and amount of time lag amounting to about 0.02 second generally exists. The wheel speed will generally exceeds 5 km/hr above the said pseudo-value.

According to our practical experiments, a higher vehicle speed will provide only a comparatively low degree of fluctuation in the slip ratio, but, in the case of medium and low wheel speeds, the variation of slip ratio will generally be apparent and substantial, resulting in a frequently encountered wheel lock or even non-effectiveness of the brake application.

Necessary braking period and the passangers drive feeling are naturally become unfavorable so far.

It is a practical and more specific object to provide a process and an apparatus for control of the brake pressure in the antiskid type braking system wherein the wheel speed is conditioned to lie within such allowance of :2-3 km/hr around the 80 percent-pseudovehicle speed.

According to this invention, the wheel speed during brake application is practically confined within such a range between 20% slip ratio and +2-3 km/hr/vehicle speed.

In this way, a maximum possible adhesive force is realized between the vehicle travelling surface and the wheel tyre surface.

Next, referring to FIG. 2, the first embodiment of the circuit arrangement embodying the main principle of the invention and adapted for the control of an automotive hydraulic brake system will be described hereinafter in detail.

In FIG. 2, the shown circuit arrangement comprises a wheel speed sensing circuit 1-] which includes a d.c. generator G-l fixedly attached to the shaft of an automotive vehicle wheel, not shown in the drawing for simplicity, for sensing occasional travelling speed of the vehicle to be braked under the control of the method and apparatus according to the invention.

This generator 0-! naturally develops a voltage output corresponding to the rotational speed of the vehicle wheel.

The positive pole of the generator is connected through a resistor Rl-l to a condenser C2-l, as shown, while the negative pole of the generator is connected to one side of a condenser Cl-l, a resistor RZ-l being connected across the generator and in paralled to said condenser Cl-l.

As commonly known to those skilled in the art, the aforementioned condenser will serveto smooth out unavoidable ripples appearing in the voltage output from the generator 6-], so as to provide a smoothening effect to the generator output.

The circuit arrangement shown in FIG. 2 comprises further a wheel deceleration sensor 11-] which includes a condenser C2-1 earthed through a resistor R3-1 while the opposite side of condenser C2-1 is connected electrically through a resistor R4-1 to the positive side of a battery B-1 and at the same time to the base electrode of a transistor Tl-l. The related circuit part constitutes a differential circuit part, serving to differentiate the smoothed output voltage from the generator G-l, so as to deliver through resistors R3-1 and R4-l to provide a proper bias voltage to the base electrode of the transistor Tl-l for keeping a base potential thereat.

The. collector electrode of transistor Tl-l is connected through a resistor RS-l to the positive pole of the battery B-1 and at the same time directly with a coupling condenser C3. The emitter of the transistor Tl-l is earthed through a resistor R6-l. The provision of transistor Tl-l, resistors R5-1 and R6-l serves for phase-conversion of the base potential of transistor Tl-l as well as for amplifying the same.

The amplified voltage is conveyed through the coupling condenser C3-1 in the form of a modified voltage as the wheel deceleration or acceleration voltage to the base of a transistor T4-l comprised in a comparator V-l to be described hereinafter.

The circuit arrangement shown in FIG. 2 further comprises as pseudowehicle setter III-l comprising a diode, the anode of which is connected with the positive pole of the generator G-l, while the cathode side of the diode is connected to the base of a transistor T3-l and at the same time earthed once through a condenser C4-1, and secondly through a series connection of resistors R7-l and R8-1, a transistor T2-1 being connected across the latter resistor R8-1.

The emitter electrode of transistor T2-1 is earthed, while the base of the latter isconnected through a paralled combination of pressure-responsive resistor 9.9-] and condenser. CS-l to the positive pole of the battery B. Although not shown, the resistor R9-l is arranged to be subjected to hydraulic brake pressure, for instance, by being immersed in the hydraulic brake pressure pipe line, not shown, and electrically connected as shown. The base of transistor T2-l is earthed through resistor RIO-1.

As may be easily supposed, the condenser C4-l accumulates the output from the generator G-1 and is adapted for discharge of the same through resistor R7-l, the equivalent resistance of transistor T2-1 and resistor R8-1.

With application of heavier brake, the resistance appearing at the resistor R9-1 will become correspondingly smaller, and vice versa. This nature of such pressure responsive resistor is highly known to those skilled in the art. Condenser C-1 will serve for smoothing the effect of the variable resistor R9-i.

The circuit arrangement shown in FIG. 4 comprises further a reference setter IV-l including a transistor T3-1, the collector of which is electrically connected to the positive side of the battery B-l, while the emitter of the sauce transistor is earthed through resistor R1 1-1, junction 1100 and a further resistor R12-l, said junction being connected, on the one hand, with said coupling condenser C3-1, and with the base of a transistor T4-1 which is included in a comparator V-l to be described.

Transistor T3-l serves for current amplifying the base potential, the amplified output being divided in its voltage through resistor R1 1-1 and Rl2-1 to 80 percent of the emitter potential at transistor T3-l, so as to provide a corresponding base potential at the transistor T4-l.

On the other hand, the variation of collector potential at the transistor Tl-l is conveyed through con denser C3-l to the base electrode of transistor T4-] to be overlapped with the base potential at T4-1. Thus, it will be seen that the base potential at T4-1 is the sum of 80 percent of the base potential at T3-l and the voltage conveyed through the condenser C3-1.

The circuit arrangement shown in FIG. 2 comprises,

as referred to above, the transistor T4-l, the collector of which is connected through a resistor Rl3-l to the positive pole of battery B l, and at the same time, through a resistor RlS-l to the base of a transistor T5-1. The emitter of transistor T4-1 is earthed through a resistor R14-1, and connected at the same time with the negative pole of the generator G-l.

The collector of transistor TS-l is connected to the positive pole of battery B-l, while the emitter of the same transistor is earthed through a resistor R16-] and connected at the same time directly to the base of a transistor T6-1.

The collector of transistor T6-l is connected directly to the positive pole of battery B-l, while the emitter of the same transistor is earthed through a solenoid S-l. Although not shown, the solenoid 8-1 is so designed and arranged, as known per se, to reduce the brake applying pressure, when the solenoid is brought into its energized state, and to restore the braking pressure when the solenoid is kept in its de-energized state. When the base voltage at the transistor T4-1 is larger than the emitter voltage at the same transistor, the transistor TS-l as well as the transistor T6-l will become conductive, so as to provide a current to solenoid S-l. On the other hand, when the base voltage of transistor T4-] is smaller than the emitter voltage of transistor T4-l, transistors T4-1 and TS-l will become nonconductive, and transistor T6-1 become also nonconductive, so as to interrupt current flow through said solenoid S-l.

The positive pole of battery 13-! is connected to resistor R4-1, RS-l, pressure-responsive resistor R9-l, resistor R134, condenser CS-l, collectors of transistors TS-l and 'l6-l and emitter of transistor TS-l, respectively. On the other hand, the negative pole of battery 8-] is connected to respective resistors R2-l, R3-1, R6-l, R84, RIO-l, RlZ-l, Rl4-1 and Rl6-l, solenoid S-l, condensers Cl-l and 03-1, the negative pole of generator 0-1 and the emitter of transistor TZ-l, and earth as shown.

The operation of the first embodiment of the circuit arrangement shown in FIG. 2 is as follows. Under normal travelling condition of the vehicle, a voltage corresponding to the wheel peripheral speed is generated at the generator (3-1, which output is subjected to smoothening effect by the condenser Cl-l. The thus smoothed voltage is divided into the following three, more specifically, the first component thereof is conveyed to transistor T4-l, so as to provide the emitter voltage thereof. The second component is subjected to a differentiation by the combination of condenser cZ-l and resistor R3-1.

The voltage subjected to a differentiation by the resistor R4 -1 is added with a bias voltage, and the resultant is subjected to phase inversion and amplification by the transistor Tl-ll, of which the collector potential variation at the transistor Tl-l is conveyed through coupling condenser C3-l to the base of transistor T4-l, thus providing a positive voltage in function of the wheel deceleration when such deceleration occurs.

When the wheel circumferential speed is subjected to an acceleration, a negative pressure will be provided in the similar way and in response to such acceleration.

Either of these voltages is conveyed to the transistor T4-1 so as to provide acorresponding base potential thereof. However, with the vehicle travelling without any brake application, the appearing deceleration and acceleration in the wheel velocity are so small that it can be neglected in practice.'

The third component is conveyed to condenser C4-l to be charged therein. When the voltage corresponding to the wheel speedand subjected to the smoothening effect as abovementioned is smaller than that of the charged voltage, the charged voltage will be discharged through the combination of resistors R7-l and R8-l, and the equivalent resistance at transistor T2-1.

Thus, it will be seen from theforegoing that under normal travelling state of the vehicle without any brake application, the charged voltage will always correspond to the wheel circumferential speed. Since, under these normal travelling condition of the vehicle, the vehicle speed and the wheel speed are substantially in coincidence with each other, a voltage corresponding to occasional vehicle speed is accumulated in the condenser C4-1, which is conveyed to transistor T3-1, when discharged, for being subjected to current amplification thereat, and subsequently is subjected to a voltage division corresponding to percent through a resistors R1 1-1 and R12-l, so as to be conveyed to transistor T4-1. For providing a corresponding base potential thereof, or more specifically, a voltage corresponding to 80 percent of the vehicle speed for constituting the base electrode at transistor T4-l. Therefore, it will be seen that the transistor T4-1 represents its base voltage comprised by a sum of pressure corresponding to 80 percent of vehicle speed and the pressure corresponding to the wheel deceleration or acceleration. On the other hand, the emitter voltage appearing at transistor T4-l corresponds to the voltage in response to occasional wheel speed, and therefore it corresponds to ,the vehicle speed under the normal travelling condition of the vehicle without any brake application.

As was referred to hereinbefore, the wheel deceleration or acceleration can be neglected under the normal vehicle travelling condition. The emitter voltage of transistor T44 will become larger than the emitter voltage of the same transistor. Therefore, transistors TS-l and T6-l will become non-conductive,'to provide non-energizing current to solenoid S-l.

Next, referring to FIG. 3, the control operation of the aforementioned circuit arrangement will be described hereinbelow.

When the wheel is applied with a braking pressure, pressure-responsive resistor R9-1 will provide a smaller resistance in response to the applied brake pressure, thus increasing corresponding the base potential at transistor T2-l, and the equivalent resistance of the same transistor will become smaller than before. Therefore, condenser'C4-1 will become liable to be discharged. As was referred to hereinbefore, condenser C4 1 is charged with a voltage corresponding to the wheel speed which is substantially equal to the occasional vehicle speed, when considered the operational condition of the circuit arrangements direct before the brake application.

When the brake is applied, the wheel speed will become correspondingly smaller and the condenser charge at C4-1 will be discharged through resistors R7-1 and R8-1, and the equivalent resistance of transistor T2-l. The discharging quantity will become larger with the increase of the larger brake application.

When the wheel is not locked, it will naturally be seen that the brake pressure and the vehicle deceleration are kept in relation to each other in a substantial degree. Therefore, when the condenser discharge rate appearing in response to the brake pressure is set so as to correspond to the vehicle deceleration degree, a voltage will be induced at the condenser C4-1 which corresponds to the occasional vehicle speed. Such voltage is called throughout the specification as pseudovehicle speed voltage. This pseudo-vehicle voltage is conveyed to transistor T3-1 so as to be subjected to current-amplification thereat, and then is subjected to the voltage division corresponding to 80 percent in its amount by resistors Rll-l and Rl2-1. This modified voltage is called throughout this specification as pseudo-vehicle speed voltage."

On the other hand, the decelerated wheel speed by virtue of the brake application will act upon the bias voltage which has been subjected to a differentiation through condenser C2-1, resistors R3-1 and R4-l and appearing through resistors R3-l and R4-1.

The thus lowered voltage is subjected to phase reversion through transistor Tl-l, resistors R5-1 and R6-l, so as to provide a 80 percent-pseudo-vehicle speed voltage, upon being increased by such degree as in relation to the wheel speed deceleration by the coupling condenser C3-l, so as to provide a proper base voltage at transistor T44. This voltage corresponds to that denoted as 80 percent-pseudo-vehicle speed plus wheel deceleration oracceleration. On the other hand, the emitter of transistor T4-l represents at this stage a voltage corresponding to the occasional wheel speed. When it is assumed that the braking force at this stage is relatively small, the wheel speed voltage is larger than the 80percent-pseudo-vehicle speed and smaller than the wheel deceleration or acceleration degree, and the emitter voltage at transistor T4-l is higher than that the base voltage .at the same transistor. Thus, the transistor T5-] becomes non-conductive, and does also the transistor T6-I. Therefore, no current will flow through solenoid S-1 and no alteration will occur in the brake applying pressure.

On the other hand, when considering the case wherein a sudden and substantial brake application is made so that a wheel lock is about to be invited, the

wheel is naturally subjected to a substantial degree of decleration and a correspondingly larger degree of speed reduction in an appreciable sudden way, until it will become smaller than the combined value of the 80 percent-pseudo-vehicle speed plus the wheel deceleration or accleration. At this stage, the emitter voltage at transistor T4-l will become smaller than the base voltage at the same transistor, resulting transistors T5-1 and T6-l turning off. Current will thus flow through solenoid S-1 and after lapse of about 0.2 second, the brake pressure will initiate to reduce.

In practice, however, as shown schematically in FIGS. 3A-3C, the brake pressure will subjected to a reduction even at a stage where the wheel speed is still larger than the 80 percent-pseudo-vehicle speed. At this stage, however, the wheel speed is subjected to a relatively large degree of deceleration, it continues to reduce in its value and the wheel speed will be accelerated at a slighty smaller than 80 percent-pseudovehicle speed by previously and properly setting of the increase ratio of 80 percent-pseudo-vehicle speed in response to the wheel speed deceleration.

With acceleration of the wheel speed, the percentpseudo-voltage will be red'u'cedby such degree as responsive to the wheel speed acceleration by the coupling condenser C3-l.' ,1 v V In this way, since the wheel speed will become larger and the sum of 80 percent-pseudo-vehicle speed'plus wheel deceleration or acceleration will become conversely smaller until the emitter voltage at transistor T4-1 becomes larger than the base voltage of the same transistor. Therefore, transistors TS-l and T6-l become non-conductive and no current will flow through solenoid S-1 and the brake pressure will take its recovery tendency upon lapse of about 0.02 second time lag.

In practice, however, as shown in FIG. 3, the brake pressure will initiate its recovery tendency even at an earlier stage where the wheel speed still remain less than the 80 percent-pseudo-vehicle speed, but, practical initiation of wheel speed deceleration will initiate at a later stage where it exceeds beyond the 80 percentpseudo-vehicle speed to a certain slight degree.

The aforementioned operational steps will be repeated while the wheel speed is dept substantially in coincidence with the 80 percent-pseudo-vehicle speed. These several operational steps will become more apparent by reference to several charts shown in FIGS. 3C-3E, which may be self explanatory.

The present embodiment is adapted for creation of the ratio between the wheel speed and the vehicle speed or that between (vehicle speed-wheel speed) and vehicle speed and the brake pressure control is preformed so as to keep it substantially constant for coinciding with 20 percent-slip ratio. For this purpose, in the present embodiment, a sum of wheel speed and vehicle speed is created, the slip ratio being kept at 20 percent. Thus, the wheel speed is controlled so as to maintain the ratio of wheel speed to vehicle speed substantially at a constant or more specifically at 0.8.

Next, referring to FIG. 4, the second embodiment of the circuit arrangement according to the invention will be described hereinafter in detail.

In FIG. 4, the shown circuit arrangement comprises a wheel speed sensing circuit 1-2 which includes a d.c.' generator G-2 fixedly attached to the shaft of an automotive vehicle wheel, not shown in the drawing for simplicity, for sensing occasional travelling speed of the vehicle to be braked under the control of the method and apparatus according to the invention.

This generator G-2 naturally develops a voltage output corresponding to the rotational speed of the vehicle wheel.

The positive pole of the generator is connected through a resistor R1-2 to a condenser C2-2, as shown, while the negative pole of thegenerator is connected to one side of a condenser C1-2, a resistor R2-2 being connected across the generator and in parallel to said condenser Cl-2.

As commonly known to those skilled in the art, the aforementioned condenser will serve to smooth out unavoidable ripples appearing in the voltage output from the generator G-2, so as to provide a smoothening effect to the generator output.

The circuit arrangement shown in FIG. 4 comprises further a wheel deceleration sensor [1-2 which includes a condenser C2-2 earthed through a resistor R3-2, while the opposite side of condenser C2-2 is connected electrically through a resistor R4-2 to the positive side of a battery B-2 and at the same time to the base elecwide of a transistor Tl-2. The related circuit part constitutes a differential circuit part, serving to differentiate the smoothed output voltage from the generator G-2, so as to deliver through resistors R3-2 and R4-2 to provide a proper bias voltage to the base electrode of the transistor T1-2 for keeping a base potential thereat. l

' The collector electrode of transistor T1-2 is connected through a resistor R5-2 to the positive pole of the battery B-2 and at the same time directly with a coupling condenser C3-2. The emitter of the transistor T1-2 is earthed through a resistor R6-2. The provision of transistor T1-2, resistors R5-2 and R6-2 serves for phase-inversion of the base potential of transistor Tl-2 as well as for amplifying the same.

The amplified voltage is conveyed through the coupling condenser C3-2 in the form of a modified voltage as the wheel deceleration or acceleration voltage to the base of a transistor T3-2 comprised in a comparator V-l to be described hereinafter.

The circuit arrangement shown in FIG. 4 further comprises as pseudo-vehicle setter III-2 comprising a diode, the anode of which is connected with the positive pole of the generator G-2, while the cathode side of the diode is connected to the base of a transistor T3-2 and at the same time earthed once through a condenser C4-2, and secondly through a series connection of resistors R7-2 and R8-2, a transistor T2-2 being connected across the latter resistor R8-2.

The emitter electrode of transistor T2-2 is earthed,

while the base of the latter is connected through a parulled combination of pressure-responsive resistor R9-2 and condenser; C5-2 to the positive pole of the battery 8. Although not shown, the resistor R9-2 is arranged to be subjected to hydraulic brake pressure, for instance, by being immersed in the hydraulic brake pressure pipe line, not shown, and electrically connected as shown. The base of transistor T2-2 is earthed through resistor RIO-2.

As may be easily supposed, the condenser C4-2, accumulates the output from the generator G-2 and is adpated for discharge of the same through resistor R7-2 the equivalent resistance of transistor T2-2 and resistor With application of heavier brake, the resistance appearing at the resistor R9-2 will become correspondingly smaller, andvice versa. This nature of such pressure responsive resistor is highly known to those skilled in the art. Condenser C5-2 will serve for smoothening the effect of the variable resistor R9-2.

The circuit arrangement shown in FIG. 4 comprises further a ratio sensor circuit IV-2 which includes an amplifier A-2, soleniods 81-2 and 82-2 and magnetic resistors M1-2 and M2-2, these are electrically connected with each other as shown, and said circuit is adapted for sensing the ratio of wheel speed to vehicle speed, as will be described more in detail hereinbelow.

As seen from the foregoing, the output voltage from the amplifier corresponds to the ratio of resistance of M2-2 to resistance of Ml-2. As symbolically described by a plurality of small arrows shown, the resistance value of magnetic resistor (magnetism responsive resistor) M2-2 will become larger with increased electromagnetic energization of solenoid 82-2. Or more specifically, it varies in response to the wheel speed.

In the similar way, the resistance value at M1-2 will vary in response to the electromagnetic energization of solenoid Sl-2. One end of the output of the amplifier A-2 is connected to the emitter of transistor T3-2, and the other end thereof is fedback to the input of the amplifier A-2 through magnetic resistor M2-2. One end of solenoid 82-2 is connected through resistor Rl-2 to generator 0-2, the other end being earthed. Owing to the large amplification rate of amplifier A-2, the output of amplifier A-2 produces voltage corresponding to resistance value of resistor M2-2 added with that of The circuit arrangement shown in FIG.'4 further comprises a ratio-setting circuit V-2 adapted for setting a ratio of wheel speed to vehicle speed which is variable according to a wheel deceleration. The base of transistor T3-2 is connectedto coupling condenser C3-2 and further to the positive pole of battery Bl-2 through resistor R1l-2, and is earthed through resistor R12-2. The emitter of transistor T3-2j is connected to output side of amplifier A-2 and is simultaneously earthed through a resistor Rl4-2. The collector of transistor T3-2 is connected to the positive pole of battery Bl-2 through a resistor R13-2, and is further connected to the base of transistor T4-2 through a resistor T5-2. The emitter of transistor T4-2 is connected to the positive pole of battery 81-2. The collector of transistor T4-2 is earthed through a resistor R16-2, and is further connected to the base of a transistor T5-2. The collector of transistor T5-2 is connected to the positive pole of battery B1-2, the emitter thereof being earthed through solenoid 83-2. When-current flows through solenoid 83-2, hydraulic pressure of wheels to be controlled is reduced, and when not, the hydraulic pressure of the same is restored. The positive pole of battery 81-2 is connected to amplifier A-2, resistors R5-2, R4-2 and R9-2, condenser C5-2, resistors Rl1-2 and RIB-2, emitter of transistor T4-2 and collector of transistor T5-2, respectively. The negative pole of battery 81-2 is earthed. The positive pole of. battery 82-2 is earthed, while the negative pole thereof is connected to amplifier A-2 and magnetic resistor Ml-2.

The operation of the second embodiment of the circuit arrangement shown in FIG. 4 is as follows. A voltage corresponding to the wheel peripheral speed is generated at the positive pole of the generator 6-2, which output is subjected to smoothening effect by the condenser Cl-2. The thus smoothed voltage is divided into the following three, more specifically, the first component thereof is applied with bias voltage by resistors R3-2 and R4-2 so as to provide base potential of transistor Tl-2 after being subjected to a differentiation by the combination of condenser C2-2 and resistor R3-2.

The phase reversion as well as current amplification is effected by transistor T1-2, resistors R5-2 and R6-2, so as to provide base potential of transistor T3-2 for the varied portion of collector potential of transistor Tl-2 by coupling condenser C3-2.

In case of wheel deceleration, the positive voltage is applied to the base of transistor '13-2, and in case of wheel acceleration, negative voltage is applied to the base of transistor T3-2.

The second component is conveyed to condenser 01-2 to be charged with the voltage corresponding to the wheel speed, and the charged voltage is discharged through resistors R7-2 and R8-2, and equivalent resistance of transistor T2-2.

Thus, it will be seen from the foregoing that under normal travelling state of the vehicle without any brake application, the charged voltage will always correspond to the wheel circumferential speed. Since, under these normal travelling condition of the vehicle, the vehicle speed and the wheel speed are substantially in coincidence with each other, a voltage corresponding to occasional vehicle speed is accumulated in the condenser C4-2, which is conveyed to transistor T3-2, when discharged, for being subjected to current amplification thereat, and subsequently is subjected to a voltage division corresponding to 80 percent through a resistors Rl1-2 and Rl2-2, so as to be conveyed to transistor T4-2. For providing a corresponding base potential thereof, or more specifically, a voltage corresponding to 80 percent of the vehicle speed for constituting the base electrode at transistor T4-2. Therefore, it will be seen that the transistor T4-2 represents its base voltage comprised by a sum of pressure corresponding to 80% of vehicle speed and the pressure corresponding to the wheel deceleration or acceleration.

The condenser C4-2 is always charged with voltage corresponding to vehicle speed. Therefore, electromagnetic energization corresponding to vehicle speed always takes place in solenoid S1-2, thus producing resistance value corresponding to vehicle speed in magnetic resistor M1-2.

In the third component, voltage corresponding to wheel speed is smoothened by resistors Rl-2 and R2-2, and condenser Cl-2, thereafter energizing solenoid S2-2. Consequently, there is always produced electromagnetic energization corresponding to wheel speed, thus producing resistance value corresponding to wheel speed in the magnetic resistor M2-2.

The output of amplifier A-2 generates voltage corresponding to the resistance value of resistor Ml-2 added with that of resistor M2-2. Namely, the voltage corresponding to wheel speed vehicle speed becomes emitter potential of transistor T3-2. The base potential of transistor is obtained by the voltage corresponding to the ratio of percent in the ratio of wheel speed to vehicle speed by dint of resistors R1l-2 and R12-2.

When the emitter potential of transistor T3-2 is larger than the base potential thereof, transistors T3-2, T4-2 and T5-2 become non-conductive, which keeps current from flowing to solenoid 83-2, and vice versa.

Under the normal travelling state of vehicle, the brake pressure is substantially nil, and condenser C4-2 stores the voltage corresponding to vehicle speed equal to wheel speed. In this case, the resistance value of resistor M1-2 is equal to that of resistor M2-2. The emitter potential of transistor T3-2 is the voltage corresponding to the value of unity in wheel speed vehicle speed. The base potential of transistor T3-2 in the voltage corresponding to the value of 0.8 in wheel speed vehicle speed. Consequently, the emitter potential of transistor T3-2 is larger than the base potential thereof, no current flows to solenoid 83-2.

Next, referring to FIG. 5, the control operation of the aforementioned circuit arrangement will be described hereinbelow.

When the wheel is applied with too high braking pressure, the wheel tends to be suddenly locked and at the same time the deceleration thereof is increased. Also the voltage of emitter potential of transistor T3-2 becomes smaller than unity, while the base potential thereof becomes to have larger value than 0.8. Finally when the emitter potential of transistor T3-2 becomes smaller than that of the base potential thereof, current flows to solenoid S3-2.'About 0.02 second after the flowing of current, the brake pressure is decreased. The wheel speed keeps on decreasing at the initial stage even if current starts to flow, but is initiated to be increased at the time when the value of wheel speed vehicle speed is slightly smaller than 0.8. The emitter potential T3-2 is gradually increased to be larger than 0.8, while the base potential thereof is decreased to be smaller than 0.8. The emitter potential becomes again larger than the base potential, thus causing no current to flow to solenoid 83-2 and restoring the brake pressure after about 0.02 second. The wheel speed is increased at the initial stage, but is once again decreased when the value of wheel speed vehicle speed exceeds 0.8. Thus, it will be seen that upon repetition of the aforementioned operations the wheel is so arranged and designed as to have approximate value of 0.8 in vehicle speed wheel speed, namely, 20 percent of slip ratio. There are several means for seeking vehicle speed in the following manners.

l. The use of the fifth wheel j 2. The sensing of deceleration in the travelling direction of the automotive vehicle 3. Inference of the road surface conditions from deceleration and acceleration of wheel.

FIGS. 6A-6B show an embodiment of using the aforementioned fifth wheel which is mounted onto the automotive vehicle. A d.c. generator 6-3 is provided in the fifth wheel. The d.c. generator generates voltage corresponding to the circumferential speed of the fifth wheel. Therefore, the d.c. generator G-3 produces voltage corresponding to vehicle speed, which is smoothened by resistors R1-3 and R2-3, and condenser Cl-3.

Before entering into a specific and detailed description of the fourth embodiment of the apparatus adapted for carrying out the method of the invention, we will illustrate at first by reference to FIG. 7 a general physical rule governing the relationship between the adhesion coefficient appearing between the tyre of a running vehicle wheel, on the one hand, and the slip ratio appearing during application of braking upon the wheel, on the other hand, said slip ratio being normally expressed by S among those who are skilled in the art and the said coefficient being, denoted by mu as is 

1. An antiskid brake control method, comprising the following steps: a. sensing a vehicle wheel speed and generating a wheel speed signal in accordance therewith; b. generating a wheel deceleration or acceleration signal as a function of said wheel speed signal; c. sensing the vehicle speed and generating a vehicle speed signal in accordance therewith; d. generating a control signal as a function of the comparison of said wheel speed signal and said vehicle speed signal when said function exceeds a predetermined slip ratio, modified by said wheel deceleration or acceleration signal, including establishing a reference signal related to a maximum coefficient of adhesion between the wheel and a traffic surface along which said wheel travels, said reference signal being related to the ratio of said wheel speed signal to said vehicle speed signal, establishing a first signal related to said wheel speed signal, and comparing said first signal with said reference signal and said wheel deceleration or acceleration signal to provide said brake pressure control signal; e. controlling said brake pressure in accordance with said control signal whereby the time lag in the reduction or restoration of said brake pressure is eliminated.
 2. The method of claim 1, including adding said wheel deceleration or acceleration signal to said reference signal.
 3. The method of claim 2 wherein said reference signal is obtained by modifying said vehicle speed signal to a value of wheel speed signal corresponding to a maximum coefficient of adhesion between the wheel and a traffic surface along which the wheel is travelling, and wherein said first signal is the vehicle wheel speed.
 4. The method of claim 2, wherein said reference signal is a ratio between the vehicle speed and the wheel speed corresponding to a maximum coefficient of adhesion between the wheel and a traffic surface along which the wheel is travelling and wherein said first signal is a value corresponding to a ratio of said vehicle speed signal to said wheel speed signal.
 5. The method of claim 2, further comprising a step for increasing the hydraulic brake pressure reduction or restoration rate when the variation in the wheel speed is larger than a predetermined value.
 6. The method of claim 5, wherein said variation in said wheel speed to be compared with said predetermined value is sensed from the absolute value of said wheel deceleration signal.
 7. The method of claim 5, wherein said variation in said wheel speed to be compared with said predetermined value is sensed from the absolute value of (wheel speed signal divided by vehicle speed signal) minus (reference signal) plus (wheel deceleration or acceleration signal).
 8. The method of claim 5, wherein said predetermined value is modified at a high frequency such that the braking pressure reduction or restoration period is variable and the braking pressure reduction anD restoration is substantially stepless.
 9. The method of claim 8, wherein the variation in said wheel speed to be compared with said high frequency is sensed from the absolute value of (wheel speed signal divided by vehicle speed signal) minus (reference signal) plus (wheel deceleration or acceleration signal).
 10. The method of claim 8, wherein said variation in said wheel speed to be compared with said high frequency is sensed from the absolute value of said wheel deceleration or acceleration.
 11. An antiskid brake control apparatus comprising: a. first circuit means for detecting a wheel speed from a generator which delivers a voltage responsive to the rotational speed of a vehicle wheel and for producing an output indicative of the wheel speed; b. second circuit means for generating a vehicle wheel deceleration or acceleration signal from the wheel speed signal; c. third circuit means for generating a vehicle speed signal by modifying the output signal from said first circuit means with the hydraulic pressure in a wheel cylinder attached to said vehicle wheel; d. fourth circuit means for generating a reference signal related to the maximum coefficient of adhesion between the wheel and the traffic surface along which said wheel travels said reference signal being related to the ratio of said wheel speed signal relative to said vehicle speed signal; e. fifth circuit means for adding said wheel deceleration or acceleration signal to said reference signal; and f. sixth circuit means for comparing the output signal from said fifth circuit with a signal related to said wheel speed signal thereby determining the direction of brake pressure control.
 12. The apparatus of claim 11, wherein said third circuit means comprises a charging circuit means for charging in response to the output signal from said first circuit means; means for sensing the hydraulic pressure in said vehicle wheel cylinder; and a discharge circuit means for discharging said charging means in accordance with the hydraulic pressure.
 13. The apparatus of claim 11, wherein said fourth circuit means comprises a voltage divider circuit for dividing the vehicle speed into a value corresponding to a wheel speed signal representing a maximum coefficient of adhesion, and wherein said sixth circuit means compares the output of said fifth circuit means with the wheel speed signal.
 14. The apparatus of claim 13, comprising eighth circuit means for comparing the absolute value of said wheel deceleration or acceleration signal with said reference signal and for reducing or restoring the hydraulic brake pressure in two stages in accordance with said comparison.
 15. The apparatus of claim 14, wherein said eight circuit means comprises a solenoid means for speeding-up the hydraulic brake pressure reduction or restoration, upon being energized in response to the wheel deceleration or acceleration being larger than said reference signal.
 16. The apparatus of claim 13, comprising ninth circuit means for generating a series of triangular signal waves; and tenth circuit means for comparing the absolute value of said wheel deceleration or acceleration signal with the output signal from said ninth circuit means such that the rate of hydraulic brake pressure decrease or increase is varied by said sixth circuit means.
 17. The apparatus of claim 16, wherein said tenth circuit means comprises a solenoid energized when the absolute value of said wheel speed deceleration or acceleration signal is less than the output signal from said ninth circuit means whereby the rate of hydraulic braking pressure decrease or increase is increased.
 18. The apparatus of claim 13, further including a valve drive circuit comprising an astable multivibrator for generating a series of pulse signals of a certain predetermined cycle; and a monostable multivibrator controlled by said wheel deceleration or acceleration signal, wherein the rate of the hydraulic brake pressure decrease or increase is variAble.
 19. The apparatus of claim 11, further comprising seventh circuit means for providing a signal corresponding to the ratio of said vehicle speed signal to said wheel speed signal wherein said reference signal corresponds to a specific ratio of said vehicle speed signal to said wheel speed signal for a maximum coefficient of adhesion, and wherein said sixth circuit means compares the output of said fifth circuit means and said seventh circuit means.
 20. The apparatus of claim 19, wherein said seventh circuit means comprises a first magnetic resistor means, the resistance of which is variable with variation in the intensity of a first solenoid energizable in response to the output signal from said third circuit means; a second magnetic resistor means, the resistance of which is variable with variation in the intensity of a magnetic field of a second solenoid energizable in response to the output signal from said first circuit means; and an amplifier means for producing a signal corresponding to a ratio of the resistance value of said second magnetic resistor means to that of said first magnetic resistor means.
 21. The apparatus of claim 19, further comprising eighth circuit means for comparing the absolute value of the output of said seventh circuit means minus the output of said fifth circuit means to said reference signal, whereby the reduction or restoration of the hydraulic brake pressure occurs in two stages wherein the reduction or restoration is determined by the output of said sixth circuit means.
 22. The apparatus of claim 21, wherein said eighth circuit means comprises a solenoid means energized when the absolute value of the difference between the output of said seventh circuit means minus the output of said fifth circuit means is larger than said reference signal whereby the rate of the hydraulic braking pressure decrease or increase is correspondingly changed.
 23. The apparatus of claim 19, comprising ninth circuit means for generating a series of triangular signal waves; and tenth circuit means for comparing the absolute value of the output signal of said seventh circuit means, minus the output signal of said fifth circuit means with said reference signal whereby the rate of the hydraulic braking pressure increases or decreases in accordance with the output of said sixth circuit means.
 24. The apparatus of claim 19, further including a valve drive circuit comprising an astable multivibrator for generation of regular pulses of a certain constant cycle; and a monostable multivibrator controlled by the absolute value of the output signal from said seventh circuit means minus the output signal from said fifth circuit means and the output of said astable multivibrator, whereby the hydraulic brake pressure increase or decrease rate is made variable.
 25. The apparatus of claim 11, wherein said sixth circuit means comprises a solenoid energized when the output signal of said fifth circuit means is larger than the signal related to said wheel speed signal, the hydraulic brake pressure decreasing when said solenoid is energized. 